Device for controlling heating boilers

ABSTRACT

A device for heating boilers (1) in heating plants comprises a means (2) for heating a heat carrying medium present in the boiler and circulating out thereof in the heating plant as well as a means (11) adapted to detect the temperature of the heat carrying medium present in the boiler and send signals to the heating means (2) to start and stop the heating of the medium when a first lower temperature level is underpassed and a second higher temperature level is exceeded, respectively, by the medium in the heating boiler (1). The device comprises further means (12) adapted to delay the start of the heating means (2) when the first temperature level is reached by the medium and this is detected by the detecting means (11).

FIELD OF THE INVENTION AND PRIOR ART

The present invention relates to a device for heating boilers in heatingplants having a means for heating a heat carrying medium present in theboiler and circulating out thereof in the heating plant as well as ameans adapted to detect the temperature of the heat carrying mediumpresent in the boiler and send signals to the heating means to start andstop the heating of the medium when a first lower temperature level isunderpassed and a second higher temperature level is exceeded,respectively, by the medium in the heating boiler.

The invention is in particular directed to devices for oil and gasboilers, and it will as a consequence thereof be discussed below forthis application for exemplifying but non-limitative purpose. Adisadvantage in common to all heating boilers for heating the rooms of abuilding and provide tap hot-water consists in that they are dimensionedso that they are able to manage conditions, in which an extremely highheating demand exists, i.e. during the coldest winter days. This meansthat the capacity of the heating boilers is utilised to the greatestextent during cold periods, but the heating boilers get over-dimensionedwith respect to the rest of the year, when the heating demand generallyis only a fraction of the amount of heat which may be supplied by theboilers, so that the efficiency sometimes will be comparatively low.

It would therefor be desired to improve the efficiency of a heatingboiler, so that it may comply with the heating demand when this isextremely high but nevertheless requires a considerably lower amount ofsupplied energy, in the oil boiler case fuel in the form of oil, forobtaining the heating comfort aimed at during periods of both high andlow heat demands, and especially in the latter case, in which theheating boiler must be considered to be strongly over-dimensioned.

SUMMARY OF THE INVENTION

Accordingly, the object of the present invention is to provide a deviceaccording to the type mentioned in the introduction, which finds aremedy to the inconveniences mentioned above by making it possible toincrease the efficiency of a heating boiler, especially when the heatdemand is low, i.e. during warm seasons.

This object is obtained by the invention by providing a device of thetype mentioned in the introduction with means adapted to delay the startof the heating means when the first temperature level is reached by themedium and this is detected by the detecting means.

Thus, by the invention it has been realized that it is possible toincrease the efficiency of a heating boiler by modifying the heatingcycles thereof. The detecting means of the device according to theinvention has the task to keep the temperature of the heat carryingmeans present in the heating boiler, i.e. usually the water, betweensaid first and second levels and by that almost static, for what reasonthe detecting means for the sake of simplicity will be called thermalrelay in the following. By the fact that the device according to theinvention delays the start of the heating means commanded by the thermalrelay the temperature of the heat carrying medium present in the heatingboiler will fall slightly, but this will not detrimentally influence theheating capacity of the heating plant, since the medium circulating inthe heating system of the building in question has a considerably lowertemperature than the medium present in the boiler, and the shunt valveco-ordinated with the boiler is able to compensate this small loweringof the temperature of the heat carrying medium of the heating boiler. Ithas been found that a prolongation of the off time of the heating boilerby a certain ratio with respect to the normal off time commanded by thethermal relay does not require a prolongation of the heating time of theheating means of a ratio being just as high should said means in theheating in both cases deliver the same power. Expressed in another waythis means that the device according to the invention leads to arequirement of a smaller amount of heat energy, i.e. fuel for obtainingthe same heating result as before, which means that the efficiency ofthe heating plant increases.

In a heating means in the form of an oil burner an additional fuelsaving is also obtained by the lower number of starts of the burner pertime unit, since a small amount of oil disappears at each start withoutgiving any real heat energy, and these small amounts of oil constitute aconsiderable part of the total fuel consumption when the heating demandis low.

By the combustion cycles of the heating boiler prolonged by the deviceaccording to the invention the boiler temperature is slightly lowered,whereby reduced energy losses are obtained, but this does not lead toany higher risk of corrosion or hot well.

According to a particularly preferred embodiment of the invention thedelay means comprises a first member adapted to measure the time betweenexceeding of the second temperature level and underpassing of the firsttemperature level following thereupon detected by the detecting means,and the delay means is adapted to determine the length of the delay timeon the basis of this time information and after this time has elapsedsend signals starting the heating means. Thanks to the completely newmethod within this technique to measure the off time of the heatingboiler, i.e. the time between switching off and on of the heating meanscommanded by the thermal relay, and utilise the result of this timemeasurement to determine the length of the delay time for the start ofthe heating boiler, an automatic adaption of the delay time to theheating demand prevailing for the moment is obtained, i.e. the delaytime becomes automatically longer in warmer seasons and shorter incolder seasons or when the heating demand suddenly increases in the formof tapping great amounts of hot-water for bath, shower and the like.Thus, an optimum prolongation of the heating cycles of the heatingboiler is always obtained in every moment, so that the heating timethereof, i.e. the burning time of the oil burner, per time unit, forinstance per day, gets so low that the conditions on the whole admit.This involves in its turn maximum improvement of the efficiency of theheating boiler-- independently of how the heating demand varies-- whileutilising the principle to prolong the heating cycles.

According to another preferred embodiment of the invention the delaymeans is adapted to determine the length of the delay time to be apre-determined ratio of the time measured by the time means. The lengthof the delay time is by that chosen to be for example 80% of the timemeasured by the time means, i.e. the time it takes for the temperatureof the heat carrying medium present in the heating boiler to sink fromthe second to the first temperature level. Thus, the length of the delaytime may be several times lower during warmer than during colderseasons.

According to a further preferred embodiment of the invention the delaymeans comprises a microprocessor which may be programmed and is adaptedto control the heating means, so that it becomes possible to change thedata being the basis of the length of the delay time according to desireand adapt the device to certain parameters of a certain heating boiler,the heating plant in question and special wishes of the user.

BRIEF DESCRIPTION OF THE DRAWINGS

With reference to the appended drawings, below follows a specificdescription of a preferred embodiment of the invention cited as anexample,

In the drawings:

FIG. 1 is a schematic view of a heating plant and illustrates a deviceaccording to a preferred embodiment of the invention, and

FIG. 2-5 are diagrams in which the temperature of the heat carryingmedium present in the heating boiler measured by the thermal relay ofthe device according to FIG. 1 is plotted versus time for illustratingthe function of the device according to the invention in some certainsituations.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

FIG. 1 illustrates schematically a device according to the inventionapplied on an oil boiler 1 having a burner 2 and a water tank 3 withwater heated by the burner 2. The heating plant comprises further a taphot-water system 4 schematically indicated by a tap and a room heatingsystem 5 with a conventional shunt valve 6, circulation pump 7 andradiators 8. The heating plant comprises further an incoming conduit 9for supply of cold water as well as a chimney 10 for discharging fluidgases resulting from the combustion of oil.

Furthermore, a thermal relay 11 is arranged to detect and react upon thetemperature of the water present in the water tank 3 and heated by theburner 2. When the temperature of this water in the immediate proximityof the thermal relay when the burner is switched off falls below a firsttemperature level, for instance 75° C., the thermal relay sends a signalin the direction of the burner so as to start this. However, the means12 of the device according to the invention for delaying the start ofthe burner 2 is connected in series to the thermal relay 11 between thelatter and the burner 2. The delay means 12 comprises a microprocessorhaving a first member adapted to measure the time elapsing between anexceeding of a second temperature level, recognised by the thermalrelay, at which level the thermal relay sends signal in the direction ofthe burner so as to turn it off, and the falling below said firsttemperature level following thereupon. The microprocessor is adapted tomultiply the time delivered by said first time measuring member by agiven factor, preferably between 0,6 and 1,0, particularly preferredabout 0,8. On receiving a signal from the thermal relay 11 indicatingthat the first temperature level has been underpassed by the water inthe water tank the microprocessor starts a count-down of the timeresulting from the multiplication by said factor in a second timemeasuring member being a part thereof and the microprocessor is adaptedto send the signal activating the burner 2 on to the burner 2 forstarting it when said time is counted down.

Thus, an extension of the off-time of the heating boiler is obtained inthis way, and the length of this extension is determined by a timemeasurement, more exactly by measuring the time elapsing between anexceeding of the second temperature level detected by the thermal relayand the underpassing of said first temperature level followingthereupon. This means that the extension of the off time of the heatingboiler will at a low energy consumption of the heating plant be longerthan at a high heat demand of the heating plant.

The device comprises further a sensor 13 adapted to detect thetemperature of the tap hot-water of the heating plant and when thelatter falls below a pre-determined temperature level, for instance 45°C., being lower than the first temperature level send signals to thedelay means 12 for stopping the delay and immediately starting theburner 2. The heating boiler may thereby deliver a sufficient amount ofheat also if the time measured by the thermal relay would be long andthe delay means by that determines a long delay time, but shortly afterthis determination a strongly increased tapping of tap hot-water, iscommenced, for instance for a shower, bath or the like.

With reference to FIG. 2-5, the result obtained by the function of thedevice according to the invention will now be explained and comparedwith a device without the delay discussed above. It is shown in FIG. 2how the temperature T measured by a thermal relay 11 may vary over thetime t when said delay is not there. This is for the rest possible toachieve in the device according to the invention by programme themultiplying factor being zero in the microprocessor of the delay means12. This means a certain numbers of starts of the burner 2 per time unitand at each start a certain operating time of the burner before, it isturned off again. The burner is started at the themperature T₀ of thehot-water of the boiler detected by the thermal relay 11 in theimmediate proximity of the thermal relay. T₀ is in this case 75° C. andthe second temperature level 80° C., but also another setting of thethermal relay, for instance 70° and 75° C., respectively, would beconceivable. The temperature T of the water in the water tank 3 measuredby the thermal relay 11 is shown in FIG. 3 plotted versus time underexactly the same heat demand conditions as in FIG. 2, but the delaymeans is here adapted to prolong the off time by 80% of the time, whichelapses from the detection of the second temperature level by thethermal relay and to the detection of the first one, so that the offtime t₁ will be 1,8× t₀. This means in this case that the temperature ofthe water in the water tank has time to fall a little bit more beforethe burner is restarted, so that the operating time of the burnernecessary for the heating to the second temperature level gets longer,but this longer operating time is not directly proportional to theprolongation of the off time of the boiler, but it ha:s turned out thatit is considerably shorter. Experiments have shown that for instance at8 starts within four hours having each an operating time of 10 minutesin the function according to FIG. 2, will correspond to five startshaving an operating time of about 12,4 minutes each in the functionaccording to FIG. 3. Since the total burning time of the oil burner,which has a constant burning power is directly proportional to the fuelconsumption, a reduction of the fuel consumption by (80-62)/80=22% isaccordingly contained. A further salving of oil is added thereto sinceat each starting moment a certain amount oil gets lost without anyappreciable delivery of heat energy. It appears from FIG. 3 that thetemperature of the hot-water at the thermal relay in practice falls veryslowly during said off time extension, and this is due to that thethermal relay is located on the heating boiler at a considerabledistance from the burner, usually in the upper part of the boiler, andit will therefor after the switching off of the burner as a consequenceof the hot-water tapping from this part of the boiler detect atemperature fall being more rapid than actually is the case for theaverage temperature of the water present in the heating boiler, so thatthe thermal relay is "cheated" and sends signals activating the burnerat the temperature level T₀, although this is not at all reached by saidaverage temperature. However the heat is after by degrees transferredfrom the water tank regions near the bottom to those located in theregion of the thermal relay, so that the temperature fall in theproximity thereof is strongly slowed down. For this reason it ispossible to extend the off time as much as mentioned above without thatthe temperature of the water in the water tank of the heating boilerfalls appreciable below the temperature T₀ set by the thermal relay.

It is illustrated in FIG. 4 what happens when the heat demand of theheating plant gets higher. A second off period 14 shown in this diagramis thought to be there during the time in which the heat demand of thedevice is comparatively high, while the off periods 15 shown before andafter this are there when the heat demand of the heating plant is low.The periods shown in FIG. 4 are in the reality not successive, althoughthis would be possible. It appears from FIG. 4 how the delay means ofthe device according to the invention thanks to the measuring of thetime Δt between the second and the first temperature level procure adelay of the start of the burner 2, which is adapted to the heat demandprevailing at that moment, i.e. a long delay at a long off time betweenthe two levels, i.e. a long Δt, and a short delay at a shorter off timebetween said levels.

It is illustrated in FIG. 5 how the device manages the situation whenafter a long off time between said levels and by that a long delay timecommanded suddenly shortly after the start of this delay time thehot-water tapping of the heating plant increases dramatically. Saidfirst temperature level of the water in the heating boiler has beenreached at the time t₁ as a consequence of which the microprocessorstarts a count-down of the delay time, which is intended to beterminated at t₂. However, as a consequence of the comparatively longtime between t₁ and t₂ and the great tapping of hot water the sensor 13will already at the time t₃ detect that the temperature of the taphot-water has fallen to 45° C. whereupon it sends signals to the delaymeans to stop the delay and immediately start the burner. It wouldotherwise without the arrangement of the sensor 13 be possible that theheating boiler would be totally drained of hot-water before the start ofthe next combustion cycle with the inconveniences connected thereto.

The microprocessor is preferably designed to store data concerningburning times of the burner, off times between said second and firsttemperature level and delay times in a memory, so that it is possiblefor the sake of comparison to run tests for the heating plant with thedelay function of the device turned on and turned off, respectively. Itmay also be of interest to study information about off and burning timesstored by the microprocessor so as to determine the optimum extension ofthe off time as a ratio of off times between said first and secondtemperature level so as to programme this ratio in the microprocessor.It is also conceivable that there is a wish to change this ratio withthe seasons, it would especially be suitable to increase this ratio alittle bit in the case that the thermal relay is set at somewhat lowertemperature levels in warmer seasons.

The invention is of course not in any way restricted to the preferredembodiment described above, but several possibilities to modificationsthereof would be apparent to a man skilled in the art without departingfrom the basic idea of the invention.

The patent claim definition "means adapted to detect the temperature ofthe heat carrying medium present in the boiler" is to be interpreted inits broadest sense, which means that it is also intended to comprise thecase in which the heating boiler is connected to a reservoir foraccumulating hot-water and the thermal relay is arranged in connectionto this reservoir.

It would also be possible to programme the microprocessor so that thisdoes not make the delay of the off time directly proportional to the offtime between said second and first temperature levels, but introducesthis off time in any special mathematical formula for calculating anddetermining the delay of the off time, although it has turned out tofunction very well with a direct proportionality.

Furthermore, the first and second time measuring means could beconstituted by one and the same clock. The time measuring means have forthe rest not necessary to indicate time, as a conventional chronometer,but they may be any means being influenced by the time and are able toobtain the delay of the off time aimed at in dependence of the timebetween the detection of the exceeding and the underpassing of saidtemperature levels by the thermal relay.

I claim:
 1. A device for controlling a boiler in a heating plant whereinthe boiler has means for heating a heat carrying medium present in theboiler and circulating out thereof in the heating plant as well as meansadapted to detect the temperature of the heat carrying medium present inthe boiler and send signals to the heating means to start and stop theheating of the medium when a first lower temperature level is reachedand a second higher temperature level is reached, respectively by themedium in the boiler, said device comprising delay means havinga firsttime measuring member arranged to measure a time signal representing thetime between the temperature of the heat carrying medium reaching thesecond higher temperature level and the temperature of the heat carryingmedium reaching the first lower temperature level following thereupon,and processor means for determining a delay time signal as a function ofthe time signal and to generate as a function of the delay time signal,a start signal for starting said heating means at a time delayed fromwhen the first temperature, level is reached by the medium.
 2. A devicefor controlling a boiler, wherein the boiler has heating means forheating a heat carrying medium and detection means for detecting thetemperature of the heat carrying medium and for generating a startsignal to start said heating means in response to the heat carryingmedium dropping below a predetermined temperature level, said devicecomprisingdelay means for delaying the start of said heating means andhaving means for measuring a time difference representing the timerequired for the heat carrying medium to change from a secondtemperature level to a first temperature level, and processor means,coupled to said detection means, and adapted for determining a time fordelaying the start of said heating means as a function of said signalrepresentative of said measured time difference and said first andsecond temperature levels of said heat carrying medium.
 3. A deviceaccording to claim 1, wherein the delay means is adapted to connect inseries between the detecting means and the heating means and is adaptedto receive from the detecting means the signal indicating when saidfirst lower temperature level of the medium is reached and to transmitto the heating means said start signal for delaying the start of theheating means.
 4. A device according to claim 1, wherein the timemeasuring member is adapted to start measuring time in response to thetemperature level of the medium reaching the second temperature leveland to terminate measuring time in response to the temperature level ofthe medium reaching the first temperature level.
 5. A device accordingto claim 1, wherein the delay means is adapted to determine the delaytime signal as a predetermined ratio of the time signal measured by thefirst time measuring member.
 6. A device according to claim 5, whereinthe delay means is adapted to delay the start of the heating means by adelay time signal being 70-90% of the time signal measured by the firsttime measuring member.
 7. A device according to claim 1, wherein thedelay means comprises a second time measuring member coupled to thetemperature detecting means and adapted to start measuring time inresponse to the temperature of the medium underpassing said firsttemperature level.
 8. A device according to claim 7, wherein the delaymeans comprises a means adapted to multiply the time measured by thefirst time measuring member by a predetermined factor, and that thesecond time measuring member is adapted to count down the time obtainedby this multiplication.
 9. A device according to claim 7, wherein thedelay means comprises a comparison means adapted to compare the timemeasured by the second time measuring member with said time signal fromthe first time measuring member and to generate the start signal forstarting the heating means in response to the second time measuringmember measuring a time substantially equivalent to a predeterminedportion of the time signal from the first time measuring member.
 10. Adevice according to claim 1, wherein the delay means comprises amicroprocessor which may be programmed and is adapted to control theheating means.
 11. A device according to claim 10, wherein themicroprocessor comprises input means for receiving input signals thatrepresent a ratio for determining the delay time signal.
 12. A deviceaccording to claim 1, wherein the device comprises a means adapted todetect the temperature of tap hot-water of the heating plant and isfurther adapted to start the heating means responsive to the temperatureof the tap hot-water reaching a pre-determined temperature level beinglower than said first temperature level.
 13. A device according to claim1, wherein the heating means includes a burner and the device is adaptedto couple to said burner.
 14. A device according to claim 1, wherein thedelay means is adapted to delay the start of the heating means by adelay time signal being 60-100% of the time signal measured by the timemeasuring member.
 15. A device according to claim 1, wherein saidprocessor means is adapted to generate a plurality of delay timesignals, each being representative of a different length of time, andsaid device further includes testing means for testing two or more ofsaid plural delay time signals to identify one delay time signalrepresentative of a substantially optimum length of time for delayingthe start of the heating means.
 16. A device according to claim 15,wherein said processor means includes memory means for storing pluralratio signals, each being representative of a different percentagevalue, and said processor element is adapted to generate the pluraldelay time signals as a function of the plural ratio signals.
 17. Adevice according to claim 15, wherein said testing means includes meansfor selectively turning on and off said delay means for operating saidboiler with and without delays respectively.
 18. Heat control apparatus,comprisingheating means for heating a heat carrying medium, circulatingmeans for circulating the heat carrying medium in a circuit, temperaturedetection means for detecting when the temperature of the heat carryingmedium reaches a first lower temperature level and reaches a secondhigher temperature level, and a processor element havinga time measuringmember arranged to measure a time signal representing the time betweenthe temperature of the heat carrying medium reaching the second highertemperature level and reaching the first lower temperature levelfollowing thereupon, means for generating a delay time signal as afunction of said time signal, and timer means, responsive to thedetection of the first temperature level being reached by the medium,for measuring a period of time representative of said delay time signaland for generating, after the measured time period, a start signal tostart the heating means.
 19. A device for controlling a boiler havingmeans for heating a heat carrying medium as well as means adapted todetect the temperature of the heat carrying medium and to send signalsto the heating means to start and stop the heating of the medium when afirst lower temperature level is reached and a second higher temperaturelevel is reached, respectively by the medium, said devicecomprisingdelay means adapted to delay the start of the heating meanswhen the first temperature level is reached by the medium and this firsttemperature level is detected by the detecting means, means fordetecting the temperature of hot water drawn from a tap and heated bythe heat carrying medium, and means for stopping the delay and forstarting the heating means responsive to the temperature of the tappedhot-water dropping below a predetermined temperature level being lowerthan said first temperature level.
 20. A device for controlling a burnerthat heats water in a water tank, comprisingtemperature detection meansfor detecting the temperature of the water and for generating a startand a stop signal representative of when the temperature of the waterreaches a first lower temperature level and reaches a second highertemperature level, respectively, a time measuring member, coupled tosaid temperature detection means, and arranged to measure a time signalrepresenting the time between said stop signal and said start signal,and a processor element adapted to determine a delay time as a functionof said time signal and to generate as a function of the delay time, adelayed start signal for starting the burner at a time delayed from whenthe first temperature level is reached by the water and this firsttemperature level is detected by the temperature detection means.
 21. Adevice for controlling a boiler having means for heating a heat carryingmedium as well as means adapted to detect the temperature of the heatcarrying medium and to send signals to the heating means to start andstop the heating of the medium when a first lower temperature level isreached and a second higher temperature level is reached, respectivelyby the medium, said device comprisingprogrammable delay means adapted togenerate a plurality of delay time signals, each being representative ofa different length of time for delaying said signal for starting saidheating means, and said device further includes testing means fortesting two or more of said plural delay time signals to identify onedelay time signal representative of a substantially optimum length oftime for delaying the start of said heating means.